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881.
为了全面深刻理解减压阀噪声的具体生成过程及现有研究基础,分析了减压阀内噪声产生的机理,总结了目前国内外减压阀噪声的研究方法,并从来源降噪和传播降噪两方面回顾了国内外降噪技术的研究现状.经过分析总结,探讨了目前研究存在的主要问题:减压阀内流动复杂、旋涡流动发生位置不明确和高速射流相互作用的影响不确定等;指出未来方向应在综合理论分析、试验研究和数值模拟的基础上,确定减压阀内噪声源位置并分析噪声指向性,明确降噪机理,进而研究降噪技术,实现根源降噪.未来对减压阀噪声的控制应从流动机理和结构创新同时着手,进而推出一套普适性低噪声阀门设计理论.研究减压阀内噪声可以为有效并针对性地降低噪声提供可靠依据. 相似文献
882.
大型LNG 储罐一旦发生泄漏,将会对周边人员和财产构成重大威胁。基于充分调研,分别从理论、试验及数值模拟3 个方面论述了国内外关于LNG 泄漏扩散的研究进展,尤其是近年来国内外在数值模拟方面的突破性研究成果。大型LNG 储罐泄漏后的气体扩散理论模型主要有高斯模型、唯象模型、箱及相似模型、浅层模型;通过LNG 泄漏试验获取了大量基础数据,主要包括气象条件参数、气云、液池燃烧的相关数据;在数值模拟方面,对LNG 泄漏气云扩散开展了大量研究,尤其是针对不同影响因素耦合作用下LNG 的泄漏扩散演变过程、气云变化形态、影响区域、爆炸范围等进行了模拟分析。通过对比分析发现,数值模拟方法具有成本低、精度高、可操性强等优点,既能有效拓展理论和试验研究成果,又能开展复杂工况下LNG 泄漏扩散的研究。对3 种方法的研究趋势进行了预测,提出大型LNG 储罐泄漏扩散的研究还需与接收站实际情况相结合,指出在今后的研究中应以数值模拟研究为主、试验与理论研究为辅。 相似文献
883.
Koji Yamane Ranee C. Mabesa-Telosa Ryosuke Tajima Nino P. M. C. Banayo Yoichiro Kato 《植物养料与土壤学杂志》2019,182(1):28-30
Simple tools for diagnosing crop nutritional status are in great demand by agricultural extension staff, particularly in low‐fertility environments. We developed the first practical method for in situ diagnosis of phosphorus (P) nutrition in field‐grown cereal crops by using a handheld colorimeter. The concentration of P in extracts from fresh leaves of lowland rice grown under various P availabilities was closely correlated with that of oven‐dried leaves measured with the standard molybdenum‐blue method in the laboratory, over a range of values from 0.319 to 1.420 mg P g ?1 DW (r = 0.885**, n = 14). It takes only 3–5 min to estimate the P concentration of plant samples using the new technique. Although not as accurate as the laboratory method, the new method can easily detect P deficiency of rice in the field (and possibly other cereal crops) without requiring costly, off‐site equipment. Thus, extension staff and agronomists can easily adopt this technique. 相似文献
884.
A. E. Hartemink 《Soil Use and Management》2008,24(4):327-330
In the 1990s and early 2000s, there was widespread pessimism on the status of soil science in most parts of the world. This was mainly due to dwindling research budgets, reduced number of students and the overall perception that soil science and pedology were dead and buried. Renewed interest in agriculture for food, feed and fuel has brought soils back onto the global research agenda. Soil erosion, nutrient depletion and pollution are key issues brought up in many recent reports by UN and other international organizations. The need for up‐to‐date and fine resolution soil information and the revival of soil research is highlighted and prioritized in several studies. There is increased interest in soils in the popular press and media, and soils have entered the policy arena. For the global soil science community, there are challenges ahead and there is a direct need to educate a new generation of soil scientists. 相似文献
885.
886.
论述了中草药提取残渣的循环再利用的应用领域,并介绍了在各个领域中中草药提取残渣的应用情况与研究现状,综合分析了中草药提取残渣再利用为实现中药材资源的循环再利用,减少环境污染的可持续性,从而为更加深入地研究中草药提取残渣用途,提高其利用价值,使中药行业走向绿色可持续发展道路提供更准确的研究思路。 相似文献
887.
888.
根据信息计量学原理运用文献分析法对《食用菌学报》1994~2008年载文数量、分类、基金论文率、论文合著、引文情况以及出版时滞等因素进行了分类和量化处理,同时对学报载文被引用情况进行统计分析,为作者和读者了解学报的发展及其影响力提供客观数据。 相似文献
889.
The role of sentinel lymph node mapping in small animal veterinary medicine: A comparison with current approaches in human medicine 下载免费PDF全文
P. Beer A. Pozzi C. Rohrer Bley N. Bacon N. S. Pfammatter C. Venzin 《Veterinary and comparative oncology》2018,16(2):178-187
The relevance of regional lymph node (LN) assessment to quantify the metastatic spread of cancer is well recognized in veterinary oncology. Evaluation of LNs is critical for tumour staging. However, sampling the correct LN may not be possible without sentinel lymph node (SLN) mapping. Methods for diagnostic imaging and intraoperative detection of SLNs are well established in human medicine, in particular, the combination of lymphoscintigraphy and intraoperative application of blue dyes. Nevertheless, alternative imaging techniques are available and have gained increasing interest. Successful implementation of these techniques in dogs have been reported in both clinical and experimental studies. This review aims to provide an overview of SLN mapping techniques in human and veterinary medicine. 相似文献
890.
Association of prognostic features and treatment on survival time of dogs with systemic mastocytosis: A retrospective analysis of 40 dogs 下载免费PDF全文
S. J. Moirano S. F. Lima K. R. Hume E. M. Brodsky 《Veterinary and comparative oncology》2018,16(1):E194-E201
Systemic mastocytosis is a rare phenomenon, with limited information regarding prognostic features and effective treatment of canine patients with this disease. The objective of this study is to determine the impact of certain features and treatments on dogs with systemic mastocytosis. The medical records of 40 dogs from 4 northeastern US veterinary hospitals, with evidence of systemic mast cell disease, were evaluated retrospectively. Variables analysed with relation to overall survival and prognostic significance included treatment protocol used, substage, presence of a cutaneous or visceral tumour, presence of multiple cutaneous Mast cell tumours, grade of the primary tumour and metastatic site(s). Dogs with metastatic disease confined to distant lymph nodes lived longer than those with circulating mast cells in the blood (P = .001), and those with metastatic disease evident in more than 2 sites had a worse prognosis than those with disease in a single location (P = .005). Additionally, administration of chemotherapeutic agents led to increased survival over prednisone therapy alone (P = .008), with the combination of lomustine, vinblastine and prednisone prolonging survival over the tyrosine kinase inhibitor, toceranib phosphate (P = .002). Presence of mast cells in the blood and/or evidence of disease in more than 2 sites indicate widespread dissemination suggesting their use as negative prognostic features. Furthermore, a chemotherapy protocol including combination lomustine and vinblastine therapy may be more effective than toceranib phosphate for the treatment of dogs with disseminated mast cell disease. Overall, patients with systemic mastocytosis have a grave prognosis and more effective treatment options are needed. 相似文献